1. Field of the Invention
The invention relates to a low-nickel austenitic stainless steel. The invention steels are resistant to corrosion, especially generalized corrosion, pitting corrosion and crevice corrosion.
2. Prior art
Patents are known which relate to steels, the composition of which contains, in proportion, the base elements such as chromium, nickel, manganese, copper and silicon, giving a structure of the austenitic type.
For example, French Patent Application No. 70/27948 relates to an austenitic steel whose composition is the following: carbon: 0.05%-0.15%; silicon: 0.3%-1.0%; manganese: 4%-12%; nickel: 0.5%-3%; chromium: 13%-16%; nitrogen: 0.05%-0.2%. This patent application discloses compositions of austenitic stainless steels with a low nickel content and relatively high manganese content, which have corrosion resistance properties equivalent to or superior to those of the conventional commercial grades having a high nickel content, such as AISI 304, 301, 201 or 202, after immersion testing in a chloride-containing medium and a test in SO.sub.2. The influence of copper, molybdenum and nickel is clearly mentioned, the nickel content having to be low, but the influence of the elements such as calcium, boron and sulfur is not mentioned.
In another example, Patent JP 54,038,217 relates to an austenitic manganese steel of the following composition: carbon: less than 0.04%; silicon: less than 1%; manganese: 6%-13%; nickel: 1.0%-3.5%; chromium: 13%-19%; niobium: less than 0.3%; copper: 1.0%-3.5%; rare earths: 0.005%-0.3%. The steel described has a corrosion resistance at least equivalent to that of stainless steel of the AISI 304 type and is highly resistant to intergranular corrosion. The elements sulfur, calcium and boron are not mentioned, nor is their influence on the various types of corrosion.
In another example, Patent JP 52,024.914 relates to an austenitic steel whose composition is the following: carbon: 0.11%-0.15%; silicon: less than 1%; manganese: 8.0%-11%; nickel: 1.0%-3.5%; chromium: 16%-18%; nitrogen: 0.05%-0.15%; copper: 0.5%-3.5%; molybdenum: less than 0.5%. It teaches that lowering the nickel content does not impair the corrosion resistance. The influence of elements such as sulfur and boron is not presented.